I find this report interesting, not sure what the deltas are but my experience was very different. I tried a Pioneer shallow mount and the same Skar mentioned above. Both sounded awful and underpowered to my relatively experienced auto sound ears used to the likes of Kicker, JL Audio, Focal and other really nice subs. The Skar was weaker than stock in deep bass at 60Hz and about the same but sloppy in low mid bass at 120hz. Stock is more balanced in this enclosure from 55Hz to 180Hz. The pioneer was massively heavy and clearly wanted way more power but it buzzed with horrible peak in high mid bass at 200Hz. I would also personally never leave an lightweight enclosure like that unbolted to avoid wasting speaker energy on kinetic loss but instead use rubber grommets, dynamat, and polyfil to lower the enclosures apparent resonant frequency and reduce vibration. From my testing and my tastes, it is hard to beat the efficiency of the stock woofer tuned to that enclosure. Better to add a larger sub and amp or do nothing in my opinion. Also noted that with door speakers replaced and fader balance 3 clicks back and sub volume all the way up, plus polyfil, the stock is actually quite inpressive for its size when fed a bit more volume.